Chapter 3 – Elements Combine to Form Compounds

Ion Charge or Combining CapacityRevisited

• The number of bonds an atom wants to form– Determined by the number of e- in the

outer shell that an element wants to donate or borrow.

Example:– Ca = +2 – Na = +1– Cl = -1

Metals vs. Nonmetals

• Metals have positive (+) charges.– Therefore, they want to donate an e- from

their outer shells.

• Most non-metals have negative (–) charges.– Therefore, they want to accept an e- into

their outer shells.

Ionic Compounds

• Atoms gain or lose electrons and form ions.• The charges of the ions are attracted to the

opposite charge; therefore a compound is produced.

Example: Na and Cl combine to form NaCl

NOTE: In covalent compounds, atoms combine by sharing electrons to form molecules.

Example: C and O share electrons to form CO

Ionic Bonds

• Lead to the formation of crystal lattices.• All the ions are attracted to all other ions in

the crystal, although nearest ions have the greatest attraction.

• Repeating pattern of negative and positive charges.

• Think in terms of ratios. NaCl is a ratio of one sodium to one chlorine, but many NaCl will form a crystal lattice.

Two Representations of Crystal Lattices

Rules for Naming IonicChemical Compounds

1. Write the name of the metal element 1st

2. Write the name of the non-metallic element 2nd (is farther right on the Periodic Table)

3. Change the ending of the non-metallic element to “ide”

Example: CaCl2

Calcium chloride

Chemical Formulas of Ionic Compounds

• Formulas contain symbols to identify each ion in an ionic compound, as well as the relative numbers of ions in the compound.

Example: NaCl – 1 sodium:1chlorine

CaF2 – 1 calcium:2 fluorines

Note: Relative numbers of each ion is a subscript to the right of the symbol

Rules for Writing Ionic Chemical Formulas

1. Write the symbol of the metal 1st

2. Write the symbol of the non-metal 2nd

3. Write in the ion charges of both symbols as superscripts to the top right of each symbol (found on the Periodic Table)

4. Drop the +/- signs and cross the ion charges and write as subscripts (to the bottom right of the symbol). The number 1 is never written.

5. Reduce, if necessary

Example of a Metal & Non-metal Combining

1. Calcium chloride (write the symbols)

2. Ca Cl (superscript combining capacities)

3. Ca 2+ Cl 1-

4. Ca 2+ Cl 1-(drop the +/- signs and cross combining capacities)

5. CaCl2

Compounds Containing Multivalent Metals

• Notice that some metallic elements have more than 1 ion charge.

• We need to use Roman Numerals to indicate which combining capacity is used.

• E.g. Copper (II) chloride = Cu +2

• E.g. Copper (I) chloride = Cu +1

Naming Note: Multivalent Metal

Use the Roman Numeral equal to the ionic charge to indicate which combining capacity was used

E.g. CuCl2

Cu1+ or Cu2+

Copper (II) chloride

E.g. Fe2O3

Fe3+ or Fe2+

Iron (III) oxide

You need to reverse cross to find combining capacities.

Reactions involving Polyatomic Ions (Radicals)

• E.g. Ammonium sulfide

• Ammonium = NH4 1+ (1+ is the ion charge)

(given on the back of the Periodic Table)

• When NH4 1+ S 2- combine, the NH4 stays together

• So, NH4 1+ S 2-

• You need to put brackets around NH4 so you can separate the digits

• (NH4)2 S

Naming Note: Polyatomic Ions

• Write the metal name first.

• Write the name of the polyatomic ion; do not change using “ide”.

Example: Sodium combines with cyanide

NaCN

Sodium cyanide

Radicals & Roman Numerals

• Copper sulfate

• Copper (II) sulfate

1.Cu SO4

2.Cu2+ SO4

2-

3.Cu2+ SO4

2-

4.Cu2(SO4)2 the 2’s reduce

5.Cu(SO4) brackets can be dropped

Types of Chemical Reactions

• Exothermic – energy is released from the reaction

Example: Atomic blast

• Memory Tip:– Exo – starts with the

letters “ex” similar to exit

Types of Chemical Reactions

• Endothermic – energy is absorbed in order for the reaction to occur

Example: cooking eggs

• Memory Tip:– Endo – starts with the

letters “en” similar to enter